A straight section $P Q$ of a circuit lies along the $X$-axis from $x=-\frac{a}{2}$ to $x=\frac{a}{2}$ and carries a steady current $i$. The magnetic field due to the section $P Q$ at a point $X=+a$ will be

• A

  proportional to $a$
• B

  proportional to $a^2$
• C

  proportional to $1 / a$
• Correct answer
  D

  zero

Solution

Magnetic field at a point on the axis of a current carrying wire is always zero.

Hence, the correct answer is option: 'D'.